1. Field of the Invention
The present invention relates to an image processing device which performs color coordinate conversion processing upon color image data.
2. Description of the Related Art
In an image input device such as a digital camera or a scanner, or an image output device such as a color printer, or an image input and output device such as a color copier, color space conversion is performed between a color space of a color signal possessed by the device itself, and a color space of a color signal which is different from the color signal possessed by the device itself; in other words, color coordinate (or colorimetric system) conversion is performed. There are various types of color space conversion, such as one in which a color space defined by three R, G, and B color signals is converted into a color space defined by a luminance signal Y and two color difference signals Cb and Cr, and another in which the color space defined by three R, G, and B color signals is converted into a color space defined by three Cy, Mg, and Ye color signals, and the like. In this kind of color space conversion, in order to perform color reproduction in the most suitable manner, it is necessary to perform delicate chromaticity correction procedures for the chromaticity signals produced as a result of the color space conversion.
As one method of performing such a chromaticity correction procedure, there is a per se known three dimensional look up table method. In such a three dimensional look up table (LUT) method, for example, when converting from a color space specified by R-G-B to a color space specified by Cy-Mg-Ye, the Cy-Mg-Ye values which correspond to all the combinations for all the tones in R-G-B are obtained by actual measurement and are stored in a memory, and conversion from the R-G-B color space to the Cy-Mg-Ye color space is performed by addressing the memory. Since with this method the color space conversion and chromaticity correction procedure are performed based upon a colossal amount of actually measured data, it is possible to perform color reproduction of high accuracy in which the characteristics of delicate colors are taken into account, but the obverse of this is that a correspondingly colossal amount of memory capacity is required. As a result there are the problems that the scale of the circuitry becomes large and the costs mount up.